As a poly-V pulley of this kind, for the usage purpose of insertion and coupling onto a shaft via a one-way clutch or a bearing, known is a poly-V pulley of a structure in which a cylindrical peripheral wall is formed, an ear for preventing a V belt from disengaging is outwardly and protrusively formed in each of the axial ends of the outer peripheral face of the peripheral wall, and poly-V grooves are formed between the both ears.
Generally, such a poly-V pulley is made of cast iron. However, the poly-V pulley made of cast iron is heavy. Moreover, the poly-V grooves are formed by cutting operations, thereby causing a problem of scattering many cut powders in workshops and worsening working environment. On the other hand, the poly-V pulley made of metal sheet, which is made of a flat plate material such as a rolled steel, has advantages: it is more durable, more lightweight and cheaper than the poly-V pulley made of cast iron.
The poly-V pulley made of metal sheet is disclosed in a gazette of Japanese Patent Laying-open No. 8-300082. The disclosed poly-V pulley has steps wherein, preparatory to forming ears for preventing a V belt (called as a belt guide in the gazette) from disengaging, on the axially both ends of a peripheral wall portion, preliminary ears (called as a portion where a guide is formed in the gazette) are formed on the both ends of the cylindrical peripheral wall by means of press process and splitting process, and the each preliminary ear whose structure is a single layer having a predetermined shape is subsequently shaped in the following step.
However, the ear having a single layer is thin so that mechanical strength thereof is inferior. In order to obtain the ear having an enough rigidity and an enough protrusive length, a thick blank is required. However, it is not easy to draw a thick blank so as to become a cup-shape with a bottom surface.
Then, an object of the present invention is to provide a poly-V pulley made of metal sheet having a superior rigidity, which makes it possible to obtain easily thick ears from the flat plate material whose thickness is not so great and which is easily drawn, and to ensure the length of the axial straight line of a bore of the cylindrical peripheral wall suitable for forcedly inserting the one-way clutch and the bearing, and a method of manufacturing the same.